Security alarm systems often use magnetic switches attached to doors and windows for detecting unauthorized openings. One type of magnetic switch utilized is a reed switch. However, these switches are subject to unauthorized manipulation through use of, for example, an external magnet. Specifically, a compact high energy magnet may be positioned in proximity to the reed switch, which will then be operated (to either open or close depending on the control scheme). Once accomplished, an intruder can open the door or window without triggering the alarm system.
A number of magnetic switches have been proposed in the past to overcome the inherent limitation and serious deficiencies of reed switches including, U.S. Pat. Nos. 5,997,873; 5,530,428; 5,332,992; 5,673,021; 5,880,659; and 6,506,987. These switches typically include a pair of spaced apart switch elements with a shiftable body (e.g., a spherical ball) movable between a first position where the ball is in simultaneous contact with both switch elements and a second position out of simultaneous contact with the switch elements. An alarm circuit may be electrically coupled to the switch elements so as to detect movement of the body. However, these switches may still be manipulated by an externally applied magnetic force.
Other systems have been presented that also offer limited protection from external magnetic manipulation including, U.S. Pat. Nos. 6,506,987; 6,603,378; and 6,803,845. While the switch arrangements in these patents represent an improvement in the field, these switch arrangements suffer from some inherent problems. For example, while offering a degree of security against external magnetic fields in one plane, these switches may still be defeated by introducing an external magnetic force in one of several or in multiple planes. Another problem presented by these switches is that they are prone to misalignment, causing problems with accurate functioning of the system. In addition, these switches may be highly sensitive to the material to which they are mounted. For example, if these switches are mounted to a steel base, a portion of the magnetic field strength may be drawn away negatively affecting system performance.
What is desired then, is a system and method that will provide an improved magnetic switching device that is essentially undefeatable by application of an externally applied magnetic field.
It is further desired to provide a system and method that provides an improved magnetic switching device that may not be defeated with the application of an external magnetic field in one of several or multiple planes.
It is still further desired to provide a system and method that provides an improved magnetic switching device that reduces sensitivity to system misalignment.
It is yet further desired to provide a system and method that provides an improved magnetic switching device that is relatively insensitive to the material to which they are mounted.